Never at JW Tumblers but at Gymboree when my daughter turned 3. Price seemed about the same. For us it worked out, because most of her friends at the time and parents we knew were at Gymboree. She got to have her favorite teacher run the party.
Since her birthday is in the Winter, this made a nice location to host several 3-4 year olds and their parents. where they could run crazy and play.
The cost covered the location, teacher (2 hours of party time), invitations, party bags (empty). We had to provide, snacks, cake, drinks and goodie bag gifts.
You have to ask yourself how much will you spend on a party that you will do somewhere else (home, park, etc) How will you keep everyone entertained and how long do you want the party to be.
So.. now that she is 5 she does not remember the party and when she looks at pictures she can not tell it is her party or a normal Gymboree free play. So the question is what do you as parents want to celebrate and remember the day.